The objectives of the proposed research are to elucidate certain virologic, epidemiologic, and clinical aspects of infection with Epstein-Barr virus (EBV), and to develop improved methods of working with this agent. Attention will be focussed on determining the sites of virus shedding (throat, urine, stool) and the duration of excretion in patients with infectious mononucleosis and in children with minor illnesses or inapparent infections. The assay system to be used is transformation of umbilical cord leukocytes; efforts will be made to simplify this method and adapt it to micro-equipment. Since EBV apparently persists for many years (if not for life) following infection, the question of reactivation such as occurs with other herpesviruses in response to various stimuli will be explored. In addition, EB virus isolates from patients with different clinical syndromes will be compared to determine whether the agent exists in more than one serotype. The virus diagnostic laboratory will be used as a source for isolates of various agents from throat washings which will also be examined to determine whether agents other than EBV can induce transformation of umbilical cord leukocytes.